# Less than prime

What is the sum of all integer values of $$n$$ satisfying $$1 \leq n \leq 100$$, such that $$n^2 - 1$$ is a product of exactly two distinct prime numbers?

Details and assumptions

The number $$12= 2 \times 2 \times 3$$ is the product of 3 (not necessarily distinct) prime numbers. With reference to this question, 12 is not the product of exactly two distinct prime numbers.

×